angular aperture

In optics, the angular aperture is a measure of an optical system's light-gathering power. It is defined by the angle subtended by the entrance pupil of the system at an object point. A larger angular aperture allows more light to enter the system, which is crucial for observing faint or distant objects, particularly in telescopes.12

The angular aperture is closely related to the aperture stop, which is the physical element that limits the diameter of the light beam passing through an optical system. In radio astronomy, techniques like aperture synthesis allow for the creation of a very large effective aperture by combining signals from multiple antennas, thereby achieving high angular resolution.13